The maintenance of the extracellular fluid volume requires a balance NaCl intake and its excretion from the body. It is well established that renal tubules and collecting ducts in the mammalian kidney reabsorb large amounts of NaCl and fluid during urine formation. However, several studies suggest that many tubular segments may also have the molecular components for net solute and fluid secretion. Therefore, it is possible that salt and fluid balance is a consequence of large scale absorption and fine-tuning by secretion. The inner medullary collecting duct (IMCD) is ideally positioned to make the final adjustments to urine before it leaves the kidney. Cells from the IMCD possess apical cystic fibrosis transmembrane conductance regulator (CFTR) Cl channels and primary cultures from rat IMCD cells display electrogenic anion secretion stimulated by cAMP. To my knowledge, NaCl and fluid secretion by the human nephron have not been adequately examined. I will investigate the extent to which human renal tubules, notably the IMCD, can actively secrete (Na)Cl and fluid and thereby contribute to the regulation of ECV.